Sherardizing
More than a hundred years ago, the Englishman Sherard Cowper-Coles developed a new galvanizing method. The method which has been named after him made it possible to create zinc layers with unique properties. The method was different primarily as regards uniformity of the layer thickness, the anti-corrosive properties and the wear resistance. In the twentieth century the method was further refined into a modern and high-quality surface treatment process.
How does it work?
Sherardising is the application of zinc coatings on steel and iron products. It involves the products being heated together with zinc powder in closed, rotating drums. Dry diffusion leads to the creation of zinc-iron alloylayers in and on the surface.
The result is a lasting, anti-corrosive, temperature and wear resistant layer which is applied uniformly over the entire surface of the product.
In contrast to other galvanizing methods, large numbers of composite forms made from spring steel, high-strength steel, cast iron, wrought metal and sinter metal can be sherardized.
The English Wikipedia page contains detailed information on diffusion galvanizing and the zinc coatings applied.
Process
Pretreatment:
Is not necessary provided the products are bright metal. Any contamination or oxidation products such as mill scale, are removed by shot blasting.
Diffusion galvanizing:
The products are heated in batches together with zinc powder in closed rotating drums. The diffusion process occurs at temperatures between 320ºC and 420ºC, during the vapour phase, and the zinc-iron alloy layers then form in and on the surface.
Coating composition:
The gamma layer with 21-27% iron forms in and on the base material while, above that, the delta compact layer forms on the surface with 8-13% iron.
Layer thickness:
Adjustable from 10 µm to 75 µm, uniform and reproducible
Follow-up treatment:
Chrome-free passivation or by means of a top coating (Duplex system)
Environment
At a time in which attention for the environment is paramount, diffusion galvanizing provides important environmental benefits in comparison to other galvanizing methods.
- No chemical pretreatment
- Entirely closed zinc process
- No production of dangerous gases
- No chemical waste flows
Sherart has been using 100% Green Power for years now.
It is therefore quite right to regard sherardizing as environmentally-responsible protection against corrosion and wear and tear.